The present invention relates generally to Storage Area Network (SAN) storage systems and, more particularly, to a method and an apparatus to migrate existing data among multiple SAN storage devices.
In recent years, the SAN storage system has been utilized to store data that are mission-critical to businesses. Host computers using the data are connected to the SAN storage systems via Fibre Channel (FC) switches. They also utilize the Fibre Channel (FC) protocol to encapsulate SCSI commands to FC frames so that they can access multiple devices connected to a SAN.
To improve the extensibility of the SAN storage system, a distributed SAN storage system extends the architecture of the SAN storage system. Such an extended SAN storage system has multiple storage devices connected to a host via an FC-SAN. The storage system migrates a data volume on a storage device to other storage devices, and switches over an I/O path for the host between those multiple storage devices. When the load of a storage system increases, the system enables to extend the whole capacity of the storage system by load-balancing for multiple volumes between multiple storage devices without replacing the storage device with one of large capacity. However, when a large number of I/O paths are configured on a SAN for the above distributed SAN storage system, there is a problem that the I/O paths reach the performance capacity of the SAN. For example, the bandwidth of a link in the SAN is used up by the multiple I/O paths for the multiple storage devices. It causes a performance decrease of I/O access. Also, the I/O paths reach the operational capacity of the SAN. For example, the number of zoning configurations for the I/O paths reaches the maximum number of zones available in the SAN. It requires re-construction of the zoning configuration and increases operational load.
In the distributed SAN storage system, when the operator extends its capacity by migrating existing volumes between multiple storage devices and by load balancing, I/O paths may reach the performance capacity and operational capacity that cause performance degradation and operational load, respectively.
U.S. Patent Application Publication No. 2010/0318692 discloses how to migrate existing data between storage systems connected to a SAN. The target storage controller is configured with at least one target volume having path-through support to a source volume of the source storage controller. An I/O path to the existing data through the target storage controller is configured. The I/O path is added to an existing I/O path connected to the existing data using an OS operational on at least one host in communication between the source and target storage controllers. The OS is adapted for I/O multipath support. After data migration, the existing I/O path is removed.